# redis-clustering

Teaches the agent how to place keys across Redis Cluster slots and move read traffic off primaries. Useful when a CROSSSLOT error shows up or you are designing keys up front.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1800 installs · ★ 170
- Author: Redis, Inc.
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/redis/agent-skills/tree/HEAD/skills/redis-clustering/SKILL.md
- Updated: 2026-09-08
- HTML: https://affpapa.org/en/nevibecode/skills/redis-clustering

## What it does

The skill covers the two things that trip up most people turning on cluster mode. First, the `CROSSSLOT` error: any command touching several keys (`MGET`, `SDIFF`, transactions, pipelines, Lua scripts) needs all of them in one slot. A hash tag fixes that, because only the part between `{` and `}` is hashed for slot assignment.

Scope the tag to the entity — `{user:1001}`, not a bare `{1001}`, or unrelated namespaces like `purchase:{1001}` and `employee:{1001}` collide on the same slot. Tag only the keys that actually need multi-key operations. Tag everything and you get hotspots, which defeats sharding. Renaming keys in production hurts, so plan tags before launch.

The second part is replica reads. In `RedisCluster` you turn them on with `read_from_replicas=True`: writes go to the primary, and a `get` may be served by a replica. For plain primary/replica setups the skill points two clients at the right hosts instead. The cost is consistency, since replicas are eventually consistent. Don't read your own writes from a replica, and keep anything needing strict freshness — balances, idempotency state — on the primary. Caches, analytics, dashboards and recommendation feeds are fine.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add redis/agent-skills --skill redis-clustering -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/redis-clustering/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/redis-clustering/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add redis/agent-skills --skill redis-clustering -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/redis-clustering/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add redis/agent-skills --skill redis-clustering -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/redis-clustering/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install redis/agent-skills redis-clustering
```

2. **Manually: put the files in place**
- File: `.github/skills/redis-clustering/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add redis/agent-skills --skill redis-clustering -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/redis/agent-skills --path skills/redis-clustering
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/redis-clustering/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add redis/agent-skills --skill redis-clustering -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/redis/agent-skills/tree/HEAD/skills/redis-clustering/SKILL.md

## When to use it
- place keys so multi-key operations stop failing
- debug a CROSSSLOT error on `MGET`, `SDIFF` or a pipeline
- build a transaction or Lua script that touches several keys in a cluster
- take read load off the primary by routing it to replicas
- decide where hash tags help and where they create hotspots

## Example prompts
- I'm getting CROSSSLOT on MGET for user:1001:profile and user:1001:settings — help me redesign the keys
- Design Redis Cluster keys for a user's cart and orders so transactions work
- Set up replica reads in RedisCluster for a dashboard, keep writes on the primary

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 46ebc51db30291c1.

BEGIN THIRD-PARTY FILE 46ebc51db30291c1
````text
---
name: redis-clustering
description: Redis Cluster and replication guidance covering hash tags for multi-key operations, avoiding CROSSSLOT errors, and reading from replicas to scale read-heavy workloads. Use when designing keys for a sharded Redis Cluster, debugging CROSSSLOT errors on MGET / SDIFF / pipelines, configuring a multi-key transaction in a cluster, or routing reads to replicas for caches, analytics, or dashboards.
license: MIT
metadata:
  author: Redis, Inc.
  version: "0.1.0"
---

# Redis Clustering

Guidance for designing keys and routing reads in a sharded Redis Cluster (and in standalone primary/replica replication). Covers the two failure modes that bite most new cluster users: `CROSSSLOT` errors on multi-key operations, and overloading primaries with read traffic.

## When to apply

- Designing keys for a Redis Cluster deployment.
- Debugging a `CROSSSLOT` error on `MGET`, `SDIFF`, transactions, or pipelines.
- Implementing transactions / Lua scripts that touch multiple keys.
- Scaling out read traffic without adding shards.

## 1. Hash tags for multi-key operations

Redis Cluster distributes keys across 16,384 slots by hashing the key name. Any command that touches **multiple keys** (`MGET`, `SDIFF`, `SUNIONSTORE`, transactions, pipelines, Lua scripts with multiple `KEYS[]`) requires all keys to live on the **same slot** — otherwise the server returns a `CROSSSLOT` error.

Hash tags force this: the part between `{` and `}` is the only thing hashed for slot assignment, so two keys sharing a hash tag always land together.

```python
# Same slot — multi-key ops work
redis.set("{user:1001}:profile",  "...")
redis.set("{user:1001}:settings", "...")
redis.lmove("{user:1001}:pending", "{user:1001}:processed", "LEFT", "RIGHT")
```

```python
# Different keys, no hash tag — CROSSSLOT on multi-key commands in cluster mode
redis.set("user:1001:profile",  "...")
redis.set("user:1001:settings", "...")
pipe = redis.pipeline()
pipe.get("user:1001:profile")
pipe.get("user:1001:settings")
pipe.execute()  # CROSSSLOT error in cluster
```

Rules of thumb:

- **Use a tag scoped to the meaningful entity**, e.g. `{user:1001}`. Avoid bare `{1001}` — unrelated namespaces (`purchase:{1001}`, `employee:{1001}`) would all collide on the same slot.
- **Only tag where you actually need multi-key ops.** Tagging everything creates hotspots and defeats the point of sharding.
````
END THIRD-PARTY FILE 46ebc51db30291c1

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